Arrays of optical fibers, or “fiber arrays,” are widely used in fields such as imaging, optical communications, remote sensing, and astronomy. One-dimensional (“1D”) fiber arrays (i.e., N-by-1 fiber arrays) integrate multiple fibers in a line in a compact optical device and offer multiplexing capability. Two-dimensional (“2D”) fiber arrays (i.e., N-by-M fiber arrays) enhance compactness and multiplexing capabilities by increasing packing density and further, provide an ability to address two dimensional spatial information in a straight-forward manner. Conventional array structures such as silicon v-grooves, glass v-grooves, glass ferrules provide precise fiber positioning yet are efficient and cost effective to manufacture.
A uncoated optical fiber end suffers from an approximate four percent (4%) Fresnel reflection which then couples back into the fiber if the fiber is perpendicularly terminated. In many applications, ends of optical fibers require different termination techniques to reduce insertion loss and/or increase return rejection. Return rejection is a concern when a laser cavity or optical amplifier is sensitive to feedback of a coupling fiber. High return loss is required in lidar (i.e., laser radar) remote sensing applications, because a small amount of surface reflection coupling back into the fiber may overwhelm as sensed return signal.
Conventional techniques for addressing return rejection and/or insertion loss include anti-reflective coatings or angle polishing/cleaving techniques. Requirements for high return loss are difficult to meet solely by applying AR coating on a terminated fiber array. Although angle termination is suitable for a single fiber or a 1D fiber array, angle terminating a 2D fiber array can be very challenging if the 2D fiber array is needed for lens imaging applications. As illustrated in FIG. 5, the fiber ends of a two-by-two fiber array have to be arranged step wise one row next to another, such that the optimal imaging can be achieved by positioning all fiber ends on a desired plane defined by the lens imaging system. As illustrated, the ends of the fibers in a given row share a common plane; but the ends of the fibers in different rows are on different planes. However, fabricating the stepwise angle terminated fiber array involves complex processes or special tools.
What is needed is an improved mechanism for terminating a two-dimensional fiber array that does not suffer the performance or manufacturing drawbacks of conventional systems.